Fix parsing of values that have trailing comments

I found that the parser wasn't properly handling values with comments. For example stanza tag/values like this:

is_a: SO:0000110 ! sequence_feature

Aren't getting matched by the TAG_VALUE regex. The branch has a test that exposes this and a fix to the code to ensure that the tags and values are added to the Stanza. Trailing comments will be stripped.

The code still lets through qualifiers and references, e.g. on synonyms.